A light source device such as a digital cinema projector includes a plurality of laser light source modules as a light source to obtain a high light output. General as a system of driving the plurality of the laser light source modules in the light source device is a drive system of electrically connecting the laser light source modules in series and evenly flowing current in each module. However, there is a problem described below in a case of electrically connecting the plurality of the laser light source modules in series and driving them.
In case of an open mode failure in a laser diode (also referred to as an LD hereinafter) (in case of a failure that the LD is not conducted and does not emit light), all of the laser light source modules connected to the defective laser light source module in series do not emit light. This means that a light output from the light source device decreases to zero, and causes a critical failure of not only the light source device but also a whole video system.
Also when the LD does not emit light while maintaining diode characteristics, generated in the defective laser light source module is heat larger than that in a normal light emission by a light emission energy. The light output of the other laser light source module needs to be increased to compensate the light output of the defective laser light source module. When a drive current is increased to increase the light output, a thermal load further increases, thereby sharply reducing reliability of the light source device.
Also in case of a half short-circuit mode failure in the LD, the drive current needs to be increased to maintain the light output as the whole light source device. When the drive current is increased, the current is concentrated in a point where the half short-circuit failure occurs, thereby leading to a burnout or a disconnection, for example. Accordingly, reliability is seriously damaged in a continuous operation of the light source device. However, in case of a complete short-circuit failure in the LD, there is no problem in operating the plurality of the laser light source modules electrically connected in series.
Proposed is a technique of continuing a light output of a light source device when any of a plurality of laser light source modules breaks down. For example, Patent Document 1 describes that when an LD breaks down, current is diverted to a substitute diode or LD parallelly connected to the LD, thereby maintaining a continuous operation of a light source device in an open failure. Patent Document 2 describes a configuration that a switching element is parallelly connected to an LD, and when voltage applied to the LD due to a failure of the LD exceeds a threshold value, the switching element diverts current flowing to the LD.